Synthesis of Crystals of Ultimate Sulfides in Sulfur Melt in a Stationary Temperature Gradient

Magnesiothermic SHS from reactive mixtures containing energy-producing additive, Mg(ClO4)2, in green mixtures was used to explore crystallization of boron carbide and its derivatives in a large SHS reactor in conditions of strong temperature gradients within the sample bulk. The addition of Mg(ClO4)2 increased a maximum combustion temperature (Tc) up to 2500°C (instead of 2000°C without the additive). The presence of gasifying agent resulted in a non-uniform distribution of combustion products. Except for the central sample area with a maximum value of Tc, the product exhibited the cell parameters corresponding to stoichiometric B4C. A two-phase material formed in the central zone was found to contain B13C2 and B25C4Mg1.42. This was explained by different temperature conditions in different areas of the sample bulk.

The paper presents the two-dimensional Lothenbach’s model of Portland cement curing based on the finite element method. The cement curing lasts for 7 days in the temperature gradient conditions ranging from 65 to −20 °C. A cement rod 7×70 cm in size is used for modelling the temperature and von Mises stress distributions. It is shown that in the temperature gradient and curing conditions, the stress maximum in Portland cement shifts toward the hot edge of the cement rod and exceeds the minimum stress level more than two times. The stress growth is significant at the interfaces between the concrete timber and the cement rod, especially at its cold edge. Such a distribution of von Mises stress is connected with the heat flow generation and their superposition with reverse heat flows. At the interfaces, superposition of the negative heat flows generates higher stresses, than superposition of the positive heat flows. The concrete timber and the interface stability are the additional factors that increase the stress level and contribute to the fracture of the pore walls.

The unconventional multi-sigmoidal kinetic behaviour of protein aggregation at a temperature gradient condition is reported in this study. To establish a feasible theory for protein aggregation kinetics at a temperature gradient condition, the spatial height of the protein solution is divided into hypothetical layers and the kinetic equations in those layers are solved. Furthermore, we endeavour to study numerically the effect of the temperature gradient on the kinetics of oligomer-mediated protein aggregation and protein inhibition.

The nonlinear free vibrations of elastically supported fiber-reinforced polymer cylindrical shells (FRPCSs) under temperature gradient conditions are investigated using both theoretical and tested techniques. A dynamic model of the FRPCSs with consideration of such complex thermal conditions is firstly established based on the first-order shear deformation theory in conjunction with Hamilton’s principle, the Galerkin method, the artificial spring technique, etc. Numerical results at room temperature and in a uniform thermal environment with classical or arbitrary boundary conditions are utilized to give a rough validation of this model. Subsequently, a thermal-vibration system is set up to measure the nonlinear natural frequencies of two FRPCS specimens subjected to four different temperature gradient conditions in free-free boundary constraints, and iterative calculations are performed to identify the temperature-dependent material properties. Finally, the detailed comparisons of calculated and experimental results provide a solid validation of the proposed model. This study offers a practical model tool to forecast the nonlinear free vibrations of the FRPCSs in a complex thermal environment, which can be readily adjusted and extended to other forms of composite shells. Also, the predicted and measured results can help assess the structural thermal-vibration behaviors when the temperature gradient effect needs to be considered. Communicated by Makoto Ohsaki.

The specific surface area (SSA) of snow is the surface area available to gases per unit mass. It is an important variable for quantifying air‐snow exchange of chemical species, and it is closely related to other variables such as albedo. Snow SSA decreases during metamorphism, but few data are available to quantify its rate of decrease. We have performed laboratory experiments under isothermal and temperature gradient conditions during which the SSA of snow samples was monitored for several months. We have also monitored the SSA of snowfalls subjected to large temperature gradients at a field site in the central Alaskan taiga. The same snow layers were also monitored in a manipulated snowpack where the temperature gradient was greatly reduced. In all cases, the SSA decay follows a logarithmic equation with three adjustable variables that are parameterized using the initial snow SSA and the time‐averaged temperature of the snow. Two parameterizations of the three adjustable variables are found: One applies to the isothermal experiments and to the quasi‐isothermal cases studied in Alaska (equitemperature (ET) metamorphism), and the other is applicable to both the laboratory experiments performed under temperature gradients and to the natural snowpack in Alaska (temperature gradient (TG) metamorphism). Higher temperatures accelerate the decrease in SSA, and this decrease is faster under TG than ET conditions. We discuss the conditions of applicability of these parameterizations and use them to speculate on the effect of climate change on snow SSA. Depending on the climate regime, changes in the rate of decay of snow SSA and hence in snow albedo may produce either negative or positive feedbacks on climate change.

At a stationary temperature gradient, the grain boundaries comprising residual melt can migrate. Their migration is governed by liquid diffusion and, in multiphase materials, depends highly on the phases present. Therefore, this phenomenon can be used for phase identification if data on metastable extensions of the corresponding phase diagram are available. Thus, we re-optimised the thermodynamic description of Tris(hydroxymethyl)aminomethane-Neopentylglycol (TRIS–NPG), a transparent peritectic alloy often used as a model alloy for metallic solidification, and used the predicted metastable liquidus and solidus curves to evaluate the grain boundary migration observations. As we found temperature gradient zone melting (TGZM) at low temperatures, the presence of the peritectic phase could be excluded even though a near-peritectic alloy had been processed. The liquid diffusivity, as a function of the position/temperature, was estimated from the TGZM velocity measurements. The data suggest that the diffusion coefficient deep in the mush is one order of magnitude smaller than that close to the liquidus temperature. This may be typical for non-dilute alloys, where the concentration of the intergranular liquid changes considerably.

Chloride diffusion through concrete is influenced by harsh environmental conditions such as high ambient temperature and relative humidity. This paper examined the influence of temperature gradient on chloride diffusion in concrete under high ambient temperature conditions. Chloride diffusion tests using cylindrical concrete samples were performed in constant temperature and temperature gradient conditions. In a temperature gradient condition, a much higher chloride concentration was measured than at constant temperatures, which could not be explained only by the mass diffusion driven by the concentration gradient. A new analytical model of chloride diffusion with the mass diffusion term including the temperature effect and the thermo-diffusion term including the temperature gradient effect was applied to the results, which showed that the thermo-diffusion contribution was significant. Using the analytical model with the mass diffusion (DCl) and thermo-diffusion (DT) coefficients, the service life of reactor containment buildings (RCBs) in nuclear power plants (NPPs) in the Middle Eastern and North African (MENA) region was estimated. The results showed that the service life of the RCBs could be reduced by the temperature gradient, indicating the possible application of the proposed analytical model.

In the study of the functionally gradient material (FGM) systems as for the high temperature structural materials, designing of these and evaluation of their thermal shock properties under the temperature gradient condition would be the most essential problems to be investigated. In this study, ZrO2/NiCrAlY functionally gradient plasma sprayed coatings were produced on the stainless steel substrates. Simple heating-cooling thermal shock testing apparatus was made, and repeated thermal shock resistance properties of the coating specimens under the temperature gradient conditions were investigated using this apparatus. Conventional thermal shock test regulated by JIS was also conducted. Moderate coating configuration for minimizing the thermal stress were estimated by the simple analytical model.The results obtained are summarized as follows, (1) Feasibility of the functionally gradient coating were verified by the temperature gradient thermal shock testing conducted using the simple apparatus made.(2) The effect of coating configuration on the repeated thermal shock resistance properties could be evaluated by the temperature gradient test condition.(3) From the results of simple numerical analysis, the moderate coating configuration profile of the functionally gradient coatings was given as the compositional distribution parameter P of less than 1.

Reinforcement corrosion induced by chloride ingress is a major durability issue in cementitious materials, particularly in harsh marine environments. Incorporating carbon nanotubes (CNTs) has emerged as a promising solution to mitigate chloride ingress. However, their performance against chloride diffusion under elevated temperatures remains unexplored. This study explores the influence of adding CNTs in cement mortars, aiming to mitigate chloride ion diffusion under temperature gradient conditions. CNTs were incorporated at 0.05%, 0.10%, and 0.15% by weight of cement in mortar specimens. Specimens were exposed to a 3% NaCl solution at room temperature of 22 °C (CT22), a high ambient temperature of 50 °C (CT50), and under a temperature gradient (TG). The experiment was carried out in two stages: the first stage aimed at finding the optimal mix based on the compressive strength, absorption, porosity, and total chloride concentration profile under the TG condition, whereas the optimal mix was thoroughly analyzed under different temperature conditions along with the assessment of the free chloride concentration profile in the second stage. The results indicated that adding 0.05% CNTs yielded the best performance, showing over a 24.6% increase in strength, about 17.5% reduction in absorption and accessible porosity, improved porous structure, and reduced chloride content. Notably, the critical chloride content based on the accelerated laboratory experimental results was substantially lower in the optimal mix than in the control, suggesting that 0.05% CNTs effectively delays chloride ion diffusion and corrosion initiation, enhancing the durability in marine environments.

Light scattering from a fluid with a stationary temperature gradient

Light scattering from a fluid with a stationary temperature gradient

Imposing an increasing stationary temperature gradient along the length of a gas chromatographic column is proposed as a technique for improving separation. Side outlet ports with control valves would allow the process to have the same advantages of programmed temperature gas chromatography without the disadvantages of temperature transients. For a simple model of gas chromatography the analysis provides expressions for temporal moments at any point along the column as a function of the temperature gradient. Reduced retention times, sharpening of peaks, and higher symmetry are predicted due to increasing the temperature gradient. The relationship to chromathermography is discussed.

On cellular spacing selection of Cu-Mn alloy under ultra-high temperature gradient and rapid solidification condition

Evolution of a mushy zone in a static temperature gradient using a volume average approach

The spontaneous transformation of a polycrystal into a single crystal at high temperatures is observed with adamantane samples. Since the plastic crystal phase at such temperatures is not elastically strained it is concluded that the process is due to the surplus of surface energy in the system. The spontaneous transformation to the equilibrium form of crystals under temperature gradient conditions is investigated. The effect is established both of the surface energy and the shape of the isothermic surfaces.